Curable silicone compositions that contain an organopolysiloxane resin and are suitable for obtaining transparent cured silicone products are known in the art. For example, Japanese Unexamined Patent Application Publication (hereinafter referred to as Kokai) 2005-042099 (equivalent to US 2005/0006794 A1) discloses a silicone rubber composition which is comprised of an organopolysiloxane having at least two aliphatic unsaturated bonds in the molecule, an organopolysiloxane of a resin structure composed of SiO2 units (hereinafter referred to as Q units), R3SiO0.5 units that contain two or three vinyl groups (hereinafter referred to as M units), and R3SiO0.5 units that may be without or with one vinyl group (however, in addition to vinyl groups, R in the above formulae may also designate univalent hydrocarbon groups without aliphatic unsaturated bonds, such as methyl groups); an organopolysiloxane with two or more silicon-bonded hydrogen atoms in the molecule; and a platinum group metal catalyst.
Kokai 2006-335857 discloses a polyorganosiloxane composition suitable for obtaining a transparent cured silicone product, the composition comprising: a linear polyorganosiloxane that contains silicon-bonded alkenyl groups and has viscosity ranging from 10 to 10,000 mm2/s at 23° C.; a branched polyorganosiloxane composed of Q units, M units with one vinyl group, and M units which are free of aliphatic unsaturated bonds; a polyalkylhydrogensiloxane consisting of Q units, M units having one silicon-bonded hydrogen atom, and M units which are free of silicon-bonded hydrogen atoms; and a platinum group metal catalyst.
Kokai 2007-131694 discloses a curable silicone composition comprising: a diorganopolysiloxane having at least two alkenyl groups in the molecule; organopolysiloxane resins of two types with different mass-average molecular weights which are composed of Q units, M units having one vinyl group, and M units which are free of unsaturated aliphatic bonds; an organopolysiloxane that contains at least two silicon-bonded hydrogen atoms in the molecule; and a hydrosilylation catalyst.
Kokai 2006-328102 (equivalent to US 2006/0264583 A1) discloses a lens-forming silicone resin composition comprising the following indispensable components and suitable for forming colorless transparent cured products: an organopolysiloxane having viscosity no less than 100 mPa·s at 25° C. and containing at least two unsaturated aliphatic bonds in the molecule; and an organohydrogenpolysiloxane having in the molecule at least three H(CH3)2SiO1/2 units; and a platinum group metal catalyst.
However, cured silicone products obtained by curing the aforementioned compositions have poor flex-resistant and can be easily damaged during molding or in assembling operations. Furthermore, they are not suitable for applications that involve bending and require that the product possess a sufficient flexural strength.